In general, as a tube material used for a refrigerant passage of an automotive heat exchanger such as radiator, evaporator and condenser, various laminated aluminum alloy sheets (hereinafter, sometimes referred to as “laminated sheet”) obtained by cladding a brazing filler material and a sacrificial material on one surface or both surfaces of a core material are used.
The laminated sheet is suitably applied as a tube material of a heat exchanger and therefore, must have certain or higher levels of strength, corrosion resistance, erosion resistance, etc., and a large number of techniques focusing on this point have been heretofore proposed.
For example, Patent Document 1 discloses a laminated sheet where in the core material, the number density of intermetallic compounds each having a predetermined size (from 0.02 to 0.2 μm) is limited to a range of 10 to 2,000/m3. According to this technique, by limiting the number density of the intermetallic compound, the strength after brazing and the corrosion resistance of the laminated sheet can be enhanced.
Patent Document 2 discloses a laminated sheet where in the core material, the number of intermetallic compounds each having a predetermined size (from 0.01 to 0.1 μm) is limited to 5 or less in a 2 μm×2 μm visual field. According to this technique, by limiting the number of intermetallic compounds in a predetermined visual field, the erosion resistance can be enhanced without deteriorating the formability of the laminated sheet.
Patent Document 3 discloses a laminated sheet where, in the core material, the average number density of precipitates in a range of 0.1 to 0.5 μm is specified to be 150/μm3 or less. According to this technique, by limiting the average number density of precipitates, the fatigue properties of the laminated sheet can be improved.